Fuel injectors for diesel, gasoline and most alternative fuel such as natural gas engines have various parts that often show wear and impede the performance of the injector. Such fuel injectors are usually, but not always located and seated in a tapered hole in the center of the cylinder head of each power assembly or unit. The upper internal working parts of the EMD locomotive injector are splash lubricated by oil thrown off by the working action of the rocker arm assemblies. The lower internal working parts are lubricated and cooled by the flow of fuel through the injector.
One of the lower internal working parts subject to wear is the injector plunger. The plunger is responsible for the atomization of the fuel which is accomplished by the high pressure created during the downward stroke of the plunger, which forces the fuel past a check valve and out through spray holes in the injector tip. The plunger is typically housed within the bushing, barrel, cylinder or housing of the fuel injector. The plunger is placed in motion within the fuel injector by an engine cam directly acting through a rocker arm and injector follower. Rotation of the plunger is accomplished by a rack and gear system mechanically linked to the engine governor that specifies or determines the quantity of fuel to be injected into the cylinder during each stroke.
The helix ridges defining the channel in the plunger, located near the bottom of the plunger, control the opening and closing of both fuel ports of the injector's plunger bushing. The rotation of the plunger regulates the time that both ports are closed during the downward stroke, thus controlling the quantity of fuel to be injected into the cylinder. As the plunger is rotated from the idling position to the full load position, the pumping stroke is lengthened, injection is generally started earlier, and more fuel is injected, as required for the necessary horsepower needed. The fuel spray atomization is accomplished by the creation of a significant increase in fuel pressure during the downward stroke of the plunger, which forces the fuel to lift the needle valve, thus delivering the high pressure fuel into the nozzle tip and out through the spray holes in the shape of numerous spray plumes into each cylinder's combustion chamber.
The tolerances between the plunger and bushing are required to be extremely tight to achieve the needed fuel pressure for the proper fuel atomization. Such tolerances are required to reduce the pumping losses of the plunger and bushing assembly which increases the overall injection efficiency. The interaction between the plunger and bushing of a mechanical fuel injector increases the pressure from the supplied pressure of 50-75 psi to a combustion chamber injection pressure of 10,000 to 20,000 psi. As can be expected, the required tight tolerances and friction between the plunger and bushing create extremely high temperatures.
The excessive heat generated during in-use service operation of the plunger can result in a bluish-purple discoloration found on the plunge's control surfaces. This discoloration or “bluing” is a visual indication of the presence of extremely high temperatures and is generally located on the lower half of the plunger's outer diameter surface, especially near the upper timing control helix. In many cases, the plungers may also have visible signs of seizing, scoring or scuffing which are also indications of the lack of lubrication. Such discoloration results in unacceptable “operational” heat-treating of the plunger's outer surface. Prolonged tempering of these surfaces often leads to unwanted deterioration or breakdown of the upper helix edges controlling the injection timing. If the helix edge material becomes more brittle, breaks down or erodes away, the injection timing changes from the original setting, thus resulting in a loss of fuel efficiency for that particular speed and load setting.
Thus, what is needed is a method and apparatus to aid in preventing excessive operational frictional heat and the consequential tempering between the plunger and bushing during the operation of the mechanical fuel injector. Furthermore, there is a need for a method and apparatus to prevent plunger tempering and the resultant deterioration or breakdown of the upper helix edges.